Morristown Medical Center

Newton Medical Center

Overlook Medical Center

Basic Dysrhythmia Course Day 1

Atlantic Health System

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Chapter 1

Anatomy and Physiology

1) Identify electrophysiology of the heart.

2) Identify the electrical conduction

structures and pathways of the heart.

3) Label an ECG complex identifying the

waveforms and intervals for segments:

PR, QRS, R-R, P-P, QT.

4) Recognize the features of normal sinus

rhythm.

5) Identify atrial rhythms.

6) Identify junctional rhythms.

Learning Objectives

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Hollow muscular organ

Lies in the space between the lungs

(mediastinum) in the chest

2/3 lies to left of midline of sternum

Location of the Heart

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Pericardium

Parietal pericardium – tough outer layer

Serous pericardium

Pericardial space contains serous fluid

Coverings of the Heart

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Endocardium

Innermost layer

Lines heart’s inner chambers

Continuous with innermost layer of vessels

Layers of the Heart Wall

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Myocardium

Middle layer

Thick, muscular layer

Responsible for pumping action

Layers of the Heart Wall

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Epicardium

Also called visceral layer of serous pericardium

External layer of heart

Contains blood capillaries, lymph capillaries,

nerve fibers, and fat

Layers of the Heart Wall

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Heart is divided into four chambers

Two upper chambers = right and left atria

Two lower chambers = right and left ventricles

Heart Chambers

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Heart contains four valves

Two sets of atrioventricular (AV) valves -Leaflet

Two sets of semilunar (SL) valves – Crescent

shaped cusps

Function

Ensure blood flows in one direction through heart

chambers

Prevent backflow of blood

Heart Valves

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AV valves separate atria from ventricles

Tricuspid valve

Lies between right atrium and right ventricle

Three separate leaflets

Mitral (bicuspid) valve

Has only two leaflets

Lies between left atrium and left ventricle

Atrioventricular (AV) Valves

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Cusps of AV valves are attached to chordae

tendineae

“Heart strings”

Attach into papillary muscles, which imbed

deeply into the endocardium

Serve as anchors

Atrioventricular (AV) Valves

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Prevent backflow of blood from the vessels

into the ventricles during diastole

Pulmonic valve

Aortic valve

Semilunar Valves

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Coronary arteries

Right

Left Main

• Left anterior descending

• Circumflex

Coronary veins

Coronary sinus

Coronary Circulation

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Sympathetic division – fight or flight

Parasympathetic division – rest and digest

Autonomic Nervous System

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Impulses sent from accelerator center in

medulla travel along sympathetic fibers

Primary neurotransmitters: norepinephrine,

epinephrine

Sympathetic Stimulation

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Sympathetic Receptor Sites

Alpha-1

Eyes, blood vessels,

bladder, male

reproductive organs

Alpha-2

Digestive system

Peripheral nervous

system

Beta-1

Heart, kidneys

Beta-2

Bronchial smooth

muscle

Skeletal blood

vessels

Dopamine

Renal, mesenteric,

and visceral blood

vessels

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Primary neurotransmitter = acetylcholine

Main effect = slowing of heart rate

Parasympathetic Stimulation

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Also called “pressoreceptors”

Specialized nerve tissue

Found in internal carotid arteries/aortic arch

Detect changes in blood pressure

Baroreceptors

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Located in internal carotid arteries and

aortic arch

Detect and respond to changes in:

Oxygen content of blood

pH

Carbon dioxide tension

Chemoreceptors

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Systole

Period during which the chamber is contracting

and blood is being ejected

Diastole

Period of relaxation during which the chamber is

filling

Cardiac Cycle

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Atrial diastole

Blood enters the right atrium

Right atrium fills and distends

• Tricuspid valve opens and the right ventricle fills

• Same sequence occurs a split second earlier in the left

heart

Left atrium receives blood from pulmonary veins

• Mitral valve opens as the left atrium fills

• Blood flows into the left ventricle

Atrial systole

Atrial kick

Atrial Systole and Diastole

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Ventricular systole

Blood is propelled through the systemic and

pulmonary circulation

AV valves close

Aortic and Pulmonic valves open

Ventricular diastole

Ventricles begin to passively fill with blood

Aortic and Pulmonic valves close

AV valves open

Ventricular Systole and Diastole

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Cardiac output

Volume of blood pumped into the aorta each

minute by the heart

Stroke volume

Amount of blood ejected from a ventricle with

each heartbeat

Cardiac Output

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Cardiac output (CO) equals stroke volume

(SV) multiplied by heart rate (HR)

CO = SV

HR

In a healthy adult, CO at rest is about

5 L/min

Cardiac Output

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Affected by change in heart rate OR stroke

volume

Factors that influence heart rate

Factors that affect stroke volume

Cardiac Output

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The percentage of blood pumped out of a

ventricle with each contraction

Used as a measure of ventricular function

A normal ejection fraction is between

50% and 65%

Ejection Fraction

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1. ________________________________________

2. ________________________________________

3. ________________________________________

4. ________________________________________

5. _________________________________________

Signs and Symptoms of

Decreased Cardiac Output:

Your Thoughts

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Signs and Symptoms of

Decreased Cardiac Output

Acute changes in

blood pressure

Acute changes in

mental status

Cold, clammy skin

Color changes in

the skin and

mucous

membranes

Crackles (rales)

Dyspnea

Dysrhythmias

Fatigue

Orthopnea

Restlessness

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Questions?

The Conduction System

Conduction system

Specialized electrical (pacemaker) cells

Arranged in a system of pathways

The Conduction System

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Primary pacemaker

Sinoatrial (SA) node

The Conduction System

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Atria Impulse leaves SA node to Bachmann’s Bundle (to

the left atrium) to simultaneously depolarize both

atria

Spreads from cell to cell across atrial muscle

The Conduction System

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Some abnormal heart rhythms

that originate in the atria result in

ineffectual atrial contraction.

What effect would this have on

atrial kick?

The Conduction System

Internodal

pathways

Impulse is spread

to AV node via

internodal

pathways

• Merge

gradually with

cells of AV

node

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AV node

Located in floor of right atrium

• Supplied by right coronary artery in most people

Delays conduction of impulse from atria to the

ventricles

• Allows time for atria to empty into ventricles

The Conduction System

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The AV node and AV bundle

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Bundle of His (AV bundle)

Connects AV node with bundle branches

Pacemaker cells have an intrinsic rate of 40 to 60

bpm

Conducts impulse to right and left bundle

branches

The Conduction System

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The Conduction System

Right bundle branch

Left bundle branch

Divides into three

fascicles

• Anterior fascicle

• Posterior fascicle

• Septal fascicle

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The Conduction System

Purkinje fibers

Receive impulse

from bundle

branches

Relay it to ventricular

myocardium

Pacemaker cells

have an intrinsic rate

of 20 to 40 bpm

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Cardiac Action Potential

Electrons

Current

Polarity

Voltage

Cardiac Action Potential

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Electrolytes

Ions

Cell membranes

Cardiac Action Potential

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Polarization (Resting)

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Depolarization = Stimulation

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Refractoriness

The period of recovery that cells need after being

discharged before they are able to respond to a

stimulus

Refractory Periods

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Refractory Periods

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Refractory Periods

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The Electrocardiogram (ECG)

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Can provide information about:

The orientation of the heart in the chest

Conduction disturbances

The electrical effects of medications and

electrolytes

The mass of cardiac muscle

The presence of ischemic damage

The ECG

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Does not provide information about the

mechanical (contractile) condition of the

myocardium

Evaluated by assessment of pulse and blood

pressure

The ECG

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Applied at specific locations on the patient's

chest wall and extremities

One end of a monitoring cable is attached

to the electrode

The other end is attached to an ECG

machine

The cable conducts current back to the

cardiac monitor

Electrodes

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EASI Lead Placement

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A lead that consists of a positive and

negative electrode

All ECG leads are technically bipolar leads

Leads I, II, and III use two distinct electrodes

Bipolar Leads

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Leads I, II, and III

Right arm electrode is always negative

Left leg electrode is always positive

Standard Limb Leads

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Einthoven’s Triangle

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Standard Limb Leads

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Augmented Limb Leads

Leads aVR, aVL, aVF

a = Augmented

V = Voltage

R = Right arm

L = Left arm

F = Foot (usually of the left

leg)

Lead aVR

Views the heart from the

right shoulder

Does not view any wall of

the heart

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Augmented Limb Leads

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Horizontal Plane Leads

Six chest (precordial

or “V”) leads view the

heart in the horizontal plane

Chest leads

V1

V2

V3

V4

V5

V6

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Chest Leads

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MCL1

Variation of chest

lead V1

Negative electrode

below left clavicle

toward left shoulder

Positive electrode

right of sternum in

4th intercostal space

Views ventricular

septum

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ECG Paper and

Systematic Rhythm

Interpretation

ECG Paper

P wave

QRS complex

T wave

U wave

PR interval

QRS duration

QT interval

Waveforms

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ECG paper is graph paper made up of small

and larger, heavy-lined squares

Smallest squares are 1 mm wide and 1 mm high

5 small squares between the heavier black lines

25 small squares within each large square

ECG Paper

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Width of each small box = 0.04 second.

Width of each large box (5 small boxes) =

0.20 second

Horizontal Axis = Time

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5 large boxes = 1 second.

15 large boxes = 3 seconds.

30 large boxes = 6 seconds.

Horizontal Axis = Time

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Size or amplitude of a waveform is

measured in millivolts (voltage) or

millimeters (amplitude).

Vertical Axis =

Voltage/Amplitude

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ECG Paper

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Terms

Baseline (isoelectric line)

Waveform

Segment

Interval

Complex

Waveforms

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P Wave: Atrial Depolarization

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Smooth and rounded

No more than 2.5 mm in height

No more than 0.11 seconds in duration

Positive in leads I, II, aVF, and V2 through V6

Normal P Wave Characteristics

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Abnormal P Waves

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Q Wave

Normal (physiologic)

Q waves

Less than 0.04 sec

Less than 1/3 the

height of R wave in

that lead

Abnormal

(pathologic) Q waves

More than 0.04 sec

More than 1/3 the

height of the

following R wave in

that lead

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R wave

The first positive, or upward, deflection following

the P wave

Always positive

S wave

A negative waveform following the R wave

Always negative

R and S waves represent depolarization of

the right and left ventricles

R and S Waves

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QRS Complex

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Measure the QRS complex with the longest

duration and clearest onset and end

In adults, the normal QRS duration is 0.11

seconds or less

Normal QRS Complex

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QRS Variations

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QRS Variations

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Portion of the ECG tracing between QRS

complex and T wave

Represents early part of repolarization of

right and left ventricles

ST Segment

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ST Segment

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ST Segment Elevation

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Represents ventricular repolarization

T Wave

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The T wave following an abnormal QRS

complex is usually opposite in direction of

the QRS

Abnormal T Waves

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P wave + PR segment = PR interval

Normally measures 0.12–0.20 sec

PR Interval

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The PR interval reflects:

Depolarization of the right and left atria (Pwave)

Spread of the impulse through the AV node, AV

bundle, right and left bundle branches, and the

Purkinje fibers (PR segment)

PR Interval

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Long PR interval (greater than 0.20 sec)

Indicates the impulse was delayed as it passed

through the atria, AV node, or AV bundle

Short PR interval (less than 0.12 sec)

May be seen when the impulse originates in the

atria close to the AV node or in the AV bundle

Abnormal PR Interval

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Portion of the ECG tracing from the beginning

of the QRS complex to the end of the T wave

Represents total ventricular activity

0.36 – 0.44 sec

QT Interval

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QT Interval = 0.36 – 0.44 seconds

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Tachycardia shortens QT intervals

Bradycardia prolongs QT Intervals

Congenital Prolongation of the QT interval

Many medications can prolong the QT

Interval

www.azcert.org

Quinolones, amiodarone, anti-psychotics, Zofran,

Albuterol, Cipro, Haldol are just a few for

example

QT Rule of Thumb

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Used to determine ventricular rate and

regularity

R-R Interval

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Used to determine atrial rate and regularity

P-P Interval

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Distortion of an ECG tracing by electrical

activity that is noncardiac in origin

Can mimic various cardiac dysrhythmias,

including ventricular fibrillation

Patient evaluation essential before initiating

any medical intervention

Artifact

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Loose electrodes

Broken ECG cables or broken wires

Muscle tremor

Patient movement

External chest compressions

60-cycle interference

Artifact—Causes

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Artifact—Loose Electrodes

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Artifact—Muscle Tremor

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Artifact—60-Cycle Interference

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Systematic Rhythm

Interpretation

Assess rhythmicity (atrial and ventricular)

Assess rate (atrial and ventricular)

Identify and examine waveforms

Assess intervals (PR, QRS, and QT) and

examine ST segments

Interpret the rhythm (and assess clinical

significance)

Systematic Rhythm

Interpretation

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Ventricular

Compare R-R intervals

Atrial

Compare P-P intervals

Rhythmicity

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Regular rhythm

Essentially regular rhythm

Irregular rhythm

Regularly irregular rhythm

Irregularly irregular rhythm

Rhythmicity - Terminology

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Assessing Ventricular

Rhythmicity

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Ventricular rate

Count the number of complete QRS complexes

within a period of 6 sec

Multiply that number by 10 to determine the

number of QRS complexes in 1 min

Six-Second Method- Can be Used in Regular or Irregular Rhythms

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Count the number of large boxes between

two consecutive waveforms (R-R interval or

P-P interval) and divide into 300

Best used if the rhythm is regular

Large Box Method-

Only in Regular Rhythms

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Large Box Method

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Sequence Method – Only in Regular Rhythms

Select an R wave that falls

on a dark vertical line

Number the next 6

consecutive dark vertical

lines as follows:

• 300, 150, 100, 75, 60,

and 50

Note where the next R

wave falls in relation to the

6 dark vertical lines

already marked—this is the

heart rate

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Count the number of small boxes between

two consecutive waveforms (R-R interval or

P-P interval) and divide into 1500

Time consuming, but accurate

Small Box Method –

Only in Regular Rhythms

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Look to see if the normal waveforms

(P, Q, R, S, and T) are present

P waves

Present?

Upright?

Do they look alike?

Is there one P wave before each QRS complex?

Identify and Examine

Waveforms

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QRS

Are QRS complexes present?

If so, does a QRS follow each P wave?

Do the QRS complexes look alike?

T waves

Does a T wave follow each QRS complex?

Does a P wave follow the T wave?

Are the T waves upright and of normal height?

Identify and Examine

Waveforms

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PR interval

QRS duration

QT interval

ST segment

Assess Intervals and

Examine Segments

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Interpret the rhythm

Specify site of origin (pacemaker site) of the

rhythm (sinus)

Specify mechanism (bradycardia) and

ventricular rate

• For example: Sinus bradycardia at 38 beats/min

Evaluate patient’s clinical presentation to

determine how he or she is tolerating the

rate and rhythm

Interpret the Rhythm

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Questions?